Optimize template rendering

Right now we use the `template` directive to render translation. This approach requires us to parse all translation in advance, even if only few translations are actually used.

We can borrow the idea from helm to introduce `include`

Start by locating the Go code that handles the `template` directive and translation rendering, then study Helm's `include` approach for comparison. Done means translations are not all parsed in advance and only translations actually used by rendering are processed.

Written by the indexing model from the issue text.